South Korea's military said it was keeping close tabs on the North amid speculation it could stage a missile launch or another nuclear test to mark the 1948 establishment of the Democratic People's Republic of Korea.

North Korea conducted its fifth nuclear test on September 9 last year, and then carried out a sixth a week ago, saying it was a hydrogen bomb that could be fitted onto a missile - prompting global condemnation and calls for further sanctions.

In July, it tested two intercontinental ballistic missiles (ICBMs) that appeared to bring much of the mainland US into range.

"The defence sector, in step with the party's Byungjin policy (of developing the economy and nuclear weapons at the same time) must make cutting-edge Juche weapons in greater quantities," the Rodong Sinmun said in an editorial, referring to the national philosophy of "Juche" or self-reliance.

The mouthpiece of the North's ruling party called for more "miracle-like events" such as the two ICBM tests to deter the United States which it said was bent on "decapitating" the nation's leader Kim Jong-Un.

"No matter how the US and its puppets kick up a ruckus, our republic, which has a strong military and the most powerful Juche bombs and weapons, and whose territory has all turned into fortresses, and all its people armed to the teeth, will remain an eternal iron-clad citadel," it said.

In another commentary, Rodong Sinmun said the US would continue receiving "gift packages in different shapes and sizes" as long as it sticks to what it said was a hostile policy against the North.

Kim himself has called the ICBM tests "gift packages" that the North was delivering to the "US bastards".